Mold-forming apparatus and method



March 1 1 9 R. s. AMALA ET AL 2,

MOLD-FORMING APPARATUS AND METHOD Filed Oct. 10, 1957 man aw U 5 4 Uni gate? gPfl sfi MOLD-FORMING APPARATUS AND METHOD Raymond S. Amala, Oak Park, and Milton J. Diamond,

Saginaw, Micln, assignors to General Motors Corporation, Detroit, Mich., a corporation of Delaware Application October 10, 1957, Serial No. 689,387

11 Claims. (CI. 22-36) This invention relates to an apparatus and process for forming sand molds or cores for foundry operations and particularly to a venting construction for such an apparatus.

As is well known, in foundry mold-blowing operations air pressure is employed to convey the molding material from a closed magazine or hopper into a cavity defined by a blowhead and one or more suitably contoured patterns. Since the molding material, which is normally principally sand, must be confined to the mold-defining areas of the pattern, the cavity to be filled constitutes an essentially closed system. During the blowing step, of course, the air in this cavity must be displaced by the molding material. Accordingly, it is necessary to provide a suitable exit for this air and at the same time confine the molding material within the cavity. A number of vent passages are therefore normally located in the blowhead or the pattern. Small metal cylinders or inserts having perforated, slotted or screened faces, which prevent the molding mix from being blown out of the molding cavity, are conventionally used in these passages.

The above-described venting arrangement is usually satisfactory. However, manymolding mixes commonly employed in mold-blowing operations contain liquid binder constituents, such as animal, vegetable or mineral oil or resins. After repeated blowing operations, such liquids condense on or otherwise coat the vent inserts. The resultant coating layer eventually causes the sand to adhere to, or cake on, the perforated surfaces of the vent inserts, ultimately forming a hard crust which decreases the efiiciency of the vents and consequently impairs the blowing operation. As a result, the molds or cores are improperly formed and are frequently of nonuniform density. This problem sometimes also exists when blowing molds or cores by the shell molding process.

Shell molds, of course, are prepared by bringing a mixture of sand and a thermosetting resin binder into contact with a heated metal pattern for a short period of time. A-layer of the molding mix adheres to the hot pattern surfaces due to the melting of the binder which bonds the sand particles together, thereby accurately reproducing pattern details. The pattern temperature and the length of time the molding material is permitted to remain in contact with the hot pattern surfaces generally determine the resulting thickness of the mold. Mold build-up time ranging from a few seconds to approximately one minute are appropriate for various applications. Pattern temperatures between about 350 F. and 450 F. are typical, but temperatures as high as 600 F. or as low as 250 F. may be advantageously employed under particular conditions.

The thin-walled mold layer thus produced is preferably then cured by heating to a temperature of approximately 300 F. to 600 F. for a short period of time, usually from a few seconds to five minutes, while in contact with the metal pattern. This baking operation converts the resinous material to a hard insoluble: binder which securely bonds the sand grains together. After curing, the mold is stripped from the pattern. The formed molds are, in effect, thin shells which have sufficient strength and rigidity to make them suitable for many casting operations.

Some shell molding mixes contain liquid binder constituents which result in the vent build-up problem referred to above. Also, the design of mold-blowing apparatus frequently is such that molding material in the vent passages becomes sutficiently hot to cause solid resin binder to melt and adhere to the surfaces of the vent inserts, thereby clogging the vents.

It is therefore a principal object of the present invention to provide a mold-forming apparatus and process in which vent inserts are automatically cleaned after each mold-blowing cycle. Such cleaning prevents formation of the aforementioned vent scabs or crusts. As a result, the efficiency of the mold-blowing machine is continuously maintained, and the resultant molds are of uniform density and otherwise properly formed.

Of course, it will be understood that the term mold, as used herein, is applied in its generic sense to mean a casting form which includes both molds and cores, this invention in no manner being limited to the former. Similarly, the word pattern is used herein as including both mold patterns and core boxes.

Other objects and advantages of this invention will more fully appear from the following detailed description of preferred embodiments thereof, reference being made to the accompanying drawing, in which:

Figure 1 is a fragmentary vertical sectional view of a mold-blowing machine embodying the invention; and

Figure 2 is a similar view of a modification of the invention shown in Figure 1.

Referring more particularly to the drawing, Figure 1 shows a mold-blowing apparatus comprising an upwardly tapered magazine 10 for containing a shell molding mixture 12. This magazine, which is located beneath a be introduced into the magazine. Attached to the lower spacers or. blow bushings 26. The blowhead is provided 7 with a plurality of vertically extending openings or ducts 28 which communicate with registering openings 30 and "32 'in the blow plate and blow bushings, respectively.

These openings, which function as blow tubes, convey the molding mix from the magazine to a mold-defining cavity 34 formed between the blowhead and a metal pattern plate 36. Of course, the blow tubes or ducts are located at appropriate positions to allow for the proper distribution of the molding mix.

A series of vent passages 38 are also drilled through the'blowhead 22 and extend vertically from the space 24 to the mold-forming cavity 34. These vent passages, which normally are of smaller diameter than the blow tube passages, provide an escape path for the air displaced from the mold-defining cavity 34 and the blow tubes or ducts 28. As shown in the drawing, the lower end of each of these vent passages contains a cup-shaped insert 40 which is provided with a multiplicity of small venting holes. The cross-sectional area of these latter holes is sufficiently small to eliminate the possibility of sand grains passing therethrough, thereby preventing the molding material from passing out of the cavity 34 T during the blowing operation.

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Anumber of tubes 42, which are hereinafter referred to as vent blowback tubes, are positioned in the space 24 between the blow plate and the blowhead and extend laterally to the edges thereof. Each of these tubes is bent at an angle of approximately 90 degrees and projects downwardly into one of the vertically extending vent passages. The lower or outlet ends 44 of the vent blowback tubes extend to within a short distance of the tops of the cup-shaped inserts 40 in the vent passages. The upper or outer ends 46 of these tubes: are connected to an air pipe or manifold 48 which conveys air under pressure for cleaning the vent inserts. In turn, of course, the air pipe is connected to a pump or other source of air pressure, not shown.

It is preferable to form the blowback tubes of sufficient length so that their outlet ends 44 will terminate about A; to /2 inch above the vent inserts 40. The inside diameters of the tubes are preferably between inch and 4 inch, depending on the size of the air vents employed. These tubes may be formed of metal or a flexible material such as rubber or plastic.

A hardened steel wear strip or plate 50 is preferably provided in the lower surface of the blowhead near its outer periphery if the blowhead is formed of aluminum or other relatively soft metal. This wear strip, which normally would extend completely around the blowhead, prevents excessive wear of the blowhead which might otherwise result because of the abrasive sand particles becoming lodged between the pattern 36 and the blowhead at their juncture 52. In this manner the wear strip ultimately functions as a seal which reduces air loss from the mold-defining cavity 34.

Coolant passages 54 may be provided within the blowhead, preferably near the outer edges of its lower moldforming surface. Liquid coolant circulated in these passages helps preclude the resinous binder of the molding material from melting and setting in the blow ducts or vent blowback passages. Also, the formed hot shell mold is thereby prevented from adhering too tightly to the blowhead and from tearing when the mold is subsequently removed from beneath the blowhead. Water, air or other suitable coolants may be employed for this purpose.

When the blowhead assembly 20 and the heated metal pattern 36 are in the mold-forming or closed position, as shown in Figure l, compressed air is fed into the magazine through the opening 16 in its top wall. This air, which is preferably introduced under approximately 75 to 110 pounds per square inch pressure, forces the molding mix 12 through the blow ducts 28-30-32 and into the mold-defining cavity 34 between the pattern 36 and the blowhead 22. With this arrangement the air is not intermixed with the molding material as the latter enters the cavity 34, but instead the compressed air functions as a ram to drive the sand-resin mix into this cavity. The air which is displaced from the mold cavity is forced upwardly through the vent passages 38 in the blowhead and into the space or chamber 24 between the blow plate 18 and the blowhead 22. This displaced air then escapes to the atmosphere around the air manifold or pipe 48.

Following the blowing operation, a time interval is allowed for the thermosetting resin binder to set on the hot pattern, a period of time ranging from a few seconds to one minute being appropriate for various applications. A mold build-up or dwell time of about seconds is usually sufiicient. After the resin has set, the pattern 36 and adhering mold shell are removed from beneath the blowhead 22. Air is then introduced under pressure through the air pipe or manifold 48 and is driven through the vent blowback tubes 42 so as to impinge forcefully against the cup-shaped vent inserts 40. Hence the above-described vent blowback system cleans the ;vents by counterflow of air, eifectively removing any molding mix adhering to the. .inserts. An air line pres- .4 sure of approximately 50 p. s. i. to 200 p. s. i. is appropriate for this purpose, and the air normally need not be applied for more than a few seconds.

In the modification of the invention shown in Figure 2, a secondary blow plate 56 is employed between the blowhead 22 and the primary blow plate 18. A number of blow bushings or spacers 60, which are similar in shape to the blow bushings shown in Figure 1, are positioned between the secondary blow plate and the blowhead to provide an interjacent space or chamber 62 communicating with the atmosphere. Air displaced from the molddefining cavity thus is permitted to escape through the vent passages 38 and this chamber. A plurality of other spacer bushings 64 are located between-the two blow plates to provide a second horizontally disposed space or chamber 66. Of course, the secondary blow plate 56 and the spacer bushings 60 and 64 are provided with appropriate aligned openings 70, 72 and 74, respectively, which communicate with the openings 28 and 30 in the blowhead and primary blow plate 18 to form the blow ducts for conveying the molding mix to the pattern.

With the modification shown in Figure 2 the air pipe 48' is affixed to the outer peripheral surfaces 68 of both blow plates and provides an air-tight joint or seal for the chamber 66 at these locations. As a result, the entire horizontal space 66 functions as an air manifold. The vent blowback tubes 44 thus may be made shorter than the tubes of the Figure 1 apparatus and are not bent. These vent blowback tubes extend downwardly through the air vent passages 38 with their lower or outlet ends terminating immediately above the perforated vent inserts 40 in the same manner as in the construction shown in Figure 1. However, their upper or inlet ends are supported in the secondary blow plate 56 and communicate with the lower horizontal air scavenging chamber 62.

In operation, the air displaced from the mold-defining cavity during the blowing step is driven upwardly through the vent passages 38 and radially outwardly through the space or chamber 62 to the atmosphere. After removing the pattern and adhering mold from beneath the blowhead, air is introduced under pressure through pipe 48' into the manifold chamber 66 and projected through the vent blowback tubes 44' against the vent inserts, thereby removing foreign matter which might otherwise clog the small perforations in these inserts.

The modification of the invention shown in Figure 2 is especially designed for forming relatively large shell molds of complicated configuration, such as multiple cavity molds. Under these conditions, it is frequently impractical or inconvenient to connect vent blowback tubes to the air pipe or manifold and have these tubes extend through the blowhead to all vents because of the number and distribution of the latter. Moreover, the arrangement shown in Figure 2 provides for a more uniform blowback or counterflow of air to clean the vents. This desirable condition results from the fact that all the vent blow back tubes may be made the same length, and the principal air pressure loss normally occurs in these tubes because of their relatively small diameter. Inasmuch as the air in the formed horizontal manifold chamber 66 is under uniform pressure throughout, the air pressure in all the vent blowback tubes likewise will be uniform.

Various modifications in the arrangement and details of the specific embodiments described and shown herein will be apparent to those skilled in the art and are contemplated.

a mold-defining cavity therebetween, a plurality of ducts extending from said magazine: through .saidblowhead to. said cavity for conveying said molding mixture thereto, avent passage extending from said cavity to the atmos-- ing a magazine for containing a molding mixture, a blow plate connected to the outlet end of said magazine, a blowhead spatially separated from said blow plate to thereby form an interjacent chamber, a pattern located beneath said blowhead, said pattern and blowhead being relatively movable into proximity to one another to form a mold-defining cavity therebetween, a plurality of ducts extending from said magazine through said blowhead to said cavity for conveying said molding mixture thereto, a-vent passage extending from said cavity to the atmosphere to permit the escape of air displaced from said cavity by said mixture, a perforated insert positioned in said vent passage, an air manifold adjacent said blowhead, and a vent blowback tube extending through said chamber, said tube having its inlet end communicating with said manifold and its outlet end extending through said vent passage and terminating adjacent said insert.

3. An apparatus for blowing foundry molds compris ing a magazine for containingamolding mixture, a blow plate connected to the outlet end of said magazine, a blowhead disposed beneath said blow plate and separated therefrom to form an interjacent chamber, a pattern located'beneath said blowhead, said pattern and blowhead being relatively movable vertically into proximity to one another to form a mold-defining cavity therebetween, a plurality of ducts extending from said magazine through said blowhead to said cavity for conveying said molding mixture thereto, a plurality of vent passages extending from said cavity to the atmosphere to permit the escape of air displaced from said cavity by said mixture, a perforated insert positioned in each of said vent passages, a vent blowback tube located in each of said vent passages and communicating with said chamber, each of said tubes having an inlet end connected to an air supply means and an outlet end terminating adjacent said insert, and means for forcing air under pressure from said air supply means and through said vent blowback tubes to cause said air to impinge on said inserts.

4. An apparatus for forming shell molds comprising a magazine for containing a molding mixture comprising sand and a thermosetting resin binder, an unheated metal blow plate connected to the outlet end of said magazine, an unheated metal blowhead disposed adjacent said blow plate, said pattern and blowhead being relatively movable into proximity with one another to form a mold-defining cavity therebetween, a plurality of dutcs extending from said magazine through said blowhead to said cavity for conveying said molding mixture thereto, a vent passage extending from said cavity to the atmosphere to permit the escape of air displaced in said cavity from said mixture, a perforated insert positioned in said vent passage, a spacer positioned between said blowhead and said blow plate to form a chamber between said plate and blowhead, an air manifold adjacent said blowhead, a vent blowback tube extending through said chamber and vent passage, said tube having its inlet end communicating with said manifold and its outlet end terminating adjacent said insert, and means for forcing air under pressure through said air manifold and said tube to cause said air to impinge on said insert and remove foreign matter thererfom.

5. An apparatus for forming foundry molds comprising a magazine .for containing a molding mixture, -a b1o w.

veying said molding material to said cavity, the outer i edges of said first blow plate and said secondary blow plate being sealed to define a chamber between saidplates, a source of air pressure connected to said chamber, a vent passage extending through said blowhead, a perforated insert positioned in said vent passage, and a vent blowback tube extending through said vent passage and secondary blow plate, the inlet end of said tubecommunicating with said chamber and the outlet end of said tube extending into proximity to said insert, the, space between said secondary blow plate and said blowhead being open to the atmosphere.

6. An apparatus for forming foundry molds comprising a magazine for containing a molding mixture, a metal blow plate connected to the outlet end of said magazine, a secondary blow plate adjacent said first blow plate and spatially separated therefrom, a blowhead disposed on the side of said secondary blow plate opposite said first blow plate and spatially separated from said secondary blow plate, a metal pattern located adjacent said blowhead, said pattern and blowhead being relatively movable into proximity with one another to form a molddefining cavity therebetween, said blow plates and said blowhead having a plurality of passages which form a duct for conveying said molding material from said magazine to said cavity, the outer edges of said first blow plate and said secondary blow plate being sealed to define an airtight chamber therebetween, a plurality of ventpassage's extending from said cavity through said blowhead to the atmosphere to permit the escape of air displaced from said cavity by said mixture, a perforated insert positioned in each of said vent passages, a vent blowback tube located in each of said vent passages, each of said tubes having an inlet end communicating with said chamber and an outlet end terminating adjacent one of said inserts, and means for forcing air under pressure through said air supply means and through said tubes to cause said air to impinge on said inserts.

7. An apparatus for blowing shell molds comprising a magazine for containing a molding mixture comprising sand and a thermosetting resin binder, an unheated metal blow plate connected to the outlet end of said magazine, an unheated metal secondary blow plate adjacent said first blow plate and forming an interjacent chamber therewith, and unheated metal blowhead disposed on the side of said secondary blow plate opposite said first blow plate and spatially separated from said secondary blow plate, said pattern and blowhead being relatively removable into proximity with one another to form a mold-defining cavity therebetween, a plurality of ducts extending from said magazine through said blowhead and blow plates to said cavity for conveying said molding mixture thereto, a plurality of vent passages extending from said cavity to the space between said blowhead and said secondary blow plate to permit the escape of air displaced from said cavity by said molding mixture, said space being open to the atmosphere and communicating through said vent passage with said cavity, a perforated insert positioned in each of said vent passages adjacent the outlet end thereof, and a vent blowback tube located in each of said vent passages and extending through said secondary blow plate and secured therein, the inlet end of said tubes each communicating with said chamber and the outlet ends of said tubes each extending into proximity to said insert, and a source of air pressure connected to said chamber to drive air under '7 pressure through said tubes into contact with said inserts to remove foreign matter therefrom:

8. A process for forming a foundry mold 'which' comprises feeding a molding material into a magazine having a blowhead attached to its outlet end, moving a metal pattern into contact with said blowhead so as to form a mold cavity therebetween, forcing said molding material by compressed air from said magazine through said blowhead into said cavity, thereafter moving said metal pattern and formed mold out of contact with said blowhead, and subsequently forcing compressed air from said blowhead in the direction of said cavity through tubes in vent passages in said blowhead to remove any molding material in said passages.

9. A process for forming a foundry mold which comprises feeding a molding mixture into a magazine having a metal blowhead attached to its outlet end, moving a metal pattern upwardly into contact with said blowhead so as to form a mold cavity therebetween, forcing said molding mixture by compressed air from said magazine through said blowhead into said cavity and driving air from said cavity through perforated inserts in venting passages in said blowhead, thereafter lowering said pattern and the formed mold out of contact with said blowhead, and subsequently forcing compressed air downwardly against said perforated inserts through tubes in said venting passages to remove foreign matter adhering to said inserts.

10. A process for forming a shell mold which comprises feeding a molding mixture containing sand and a thermosetting binder into a magazine having an unheated blowhead attached to its outlet end, moving a heated pattern into proximity to said blowhead so as to form a mold cavity therebetween, forcing said molding mixture by compressed air from said magazine through 3 said blowhead into said cavity so as to fully occupy said cavity, permitting the molding mixture to remain insaid cavity for a period'of'time sufficient to meltsaid binder and bond said sand into a solid mold shell having walls with a thickness equal to the distance betweensaid blowhead and said pattern, thereafter moving said heated pattern from the vicinity of said blowhead, and subsequently forcing compressed air toward said cavity through tubes in vents in said blowhead to remove any molding mixture adhering to said vents.

11. A process for forming a shell mold which comprises feeding a molding mixture containing sand and a thermosetting resin binder into a magazine having an unheated metal blowhead attached to its outlet end, moving a heated metal pattern upwardly into contact with said blowhead so as to form a mold cavity therebetween, forcing said molding mixture by compressed air from said magazine through said blowhead into said cavity so as to fully occupy said cavity and drive air therefrom through perforated inserts in venting, passages in said blowhead, permitting said molding mixture to remain in said cavity for a period of time sufi'icient to melt said binder and bond said sand into a solid shell mold having walls with a thickness equal to the distance between said blowhead and said pattern, thereafter lowering said heated pattern and adhering shell mold layer out of contact with said blowhead, and subsequently forcing compressed air downwardly through tubes in said venting passages to remove any molding mixture adhering to said perforated inserts.

References Cited in the file of this patent UNITED STATES PATENTS 1,524,117 Tscherning Jan. 27, 1925 2,785,447 Anderson Mar. 19, 1957 2,815,550 Valyi Dec-10, 1957 

